1. Field of Invention
The present invention relates to a circuit and a method of estimating a pulse frequency of nozzle in an ink-jet head, and more particularly to a circuit and a method of estimating a pulse frequency of nozzle in an ink-jet head to provide real-time pulse frequency of nozzles for the temperature control of nozzles in an ink-jet head.
2. Related Art
The printing quality of a thermal bubble ink-jet printer is closely related to the temperature control of the ink-jet head. The ink inside an ink chamber is heated into bubbles by a thermally resistive layer and then ink-jets from the nozzles. The temperature of the ink-jet head greatly influences sizes of ink drops. During the ink-jet printing, the change in the temperature of the ink-jet head causes non-uniform sizes of the ink drops, which deteriorates the printing quality. Therefore, the temperature control of the ink-jet head is very important.
A conventional method of controlling the temperature of the ink-jet head adds a thermistor as a temperature sensor to measure the change in the temperature of the ink-jet head and perform the temperature control according to the temperature change. However, the thermistor measures the temperature of the whole ink-jet head, rather than the temperature of individual nozzles. Therefore, it is hard to estimate sizes of ink drops for each nozzle, and to compensate the drop loss caused by the temperature change of the individual nozzles. This is a critical issue particularly in high-precision ink-jet applications, such as ink-jet print color filters or polymer electro-actuated illumination elements that require highly precise control of ink volume. Not only the average temperature but also the temperature change for each nozzle needs to be compensated.
In the light of manufacturing technology and cost, using a thermistor to measure each nozzle is not practical. Therefore, an approach using a percentage of each nozzle per unit time is a basis for measuring the temperature change. The higher the using frequency of the nozzle per unit time, the higher the temperature is, and vice versa. U.S. Pat. No. 4,791,435 discloses using a counter to count ink-jet pulse of each nozzle. The prior art is only applied in the time the disclosure was proposed because the number of nozzles of the conventional ink-jet head is small while the circuit of the counter is not big. However, '435 is not suitable for current ink-jet heads that have a large number of nozzles. Otherwise, the circuit for the counter must be huge.
Another approach to estimate the pulse frequency of the nozzle is disclosed in U.S. Pat. No. No. 5,168,284. Image data are dot-to-dot checked before being printed. Each pixel corresponds to a nozzle, and then all nozzles are summed up. This method has to ‘dot-to-dot’ check all the image data, which woks with low efficiency.